The Role of Leptin in Reproduction and Fertility

Leptin was originally identified as a peripheral satiety signal made by fat cells and it was proposed that as fat accumulates leptin is secreted proportionally. Leptin then crosses the blood brain barrier and signals to the hypothalamus suppressing appetite and increasing energy expenditure as it rises. It is evident that if the leptin gene or its receptor is disrupted them morbid obesity occurs. However, obesity in humans is very rarely caused by a disruption of the leptin gene or its receptor, and in many species a good correlation exists between leptin concentrations in plasma with the degree of obesity. This early finding was unexpected and led to the leptin resistance hypothesis. Further studies have revealed that leptin actually appears to be almost ubiquitously expressed in many tissues. Unfortunately despite the accumulation of a vast literature leptin still appears to be regarded as a peripheral satiety signal although the data to support this hypothesis is not substantial.